Respect is Earned 07 - Good introductory PPV
Driven 07 - Must see Danielson vs. Nigel. Out of Print, but worth tracking down.
Man Up - One of the best ROH's shows of all time. Unforgettable Ladder War.
Undeniable - Big event, not the best PPV this year.
Rising Above 07 - Nigel vs Aries, in a must see, almost 5 star match.
Take No prisoners 08 - Again must see main event.
Respect is Earned II - Solid show
New Horizons - I was here live, i thought it was an OK show. Not the best PPV.
Driven II - Rare show. Some matches.
Rising Above 2008 - Best PPV of 2008. Climax of two major fueds in 2008.
Final Battle 2009 - First Ippv - Very good with memorable moments and good matches.
Big Bang - Solid PPV. Fun match event, weak lower card.
Death Before Dishonor 2010- One of the greatest ROH Shows. Must see
Glory By Honor 9 - Epic event, decent wrestling. Awesome show live.
Final Battle 2010 - Another must see show. Two awesome final matches.

So basically there is 3 era's of PPV's 2007, 2008 and the IPPV series. 2007 had excellent build up to the next show, and some epic main events. In 2008 they didn't put as much emphasis on the PPV's and they were putting them in B markets like Detroit, and i think Boston got one as well. Some great matchups, but the only one that really stood out to me with Rising Above. Great booking that year as well with the AOTF/Aries fued, and Danielson chasing the reigning champ Nigel. Good stuff. The IPPV series has been very solid. You easily get your moneys worth, and these are what Live PPV's should be. Shocking events, good/great matches, solid build up. ROH hit on all cylinders with these shows, so picking the PPV's to watch is a great starting point. Not a bad show with any of these. Certainly there are great DVD's too, but starting with the PPV's works imo. Maybe not the most in depth review of each ppv, but i think with this narrative below you get the idea.

I thought Caged Collision was mediocre and Take No Prisoners 09 was just slightly above average. But if you're just getting into ROH, you'll probably like them more than someone as jaded as me.

Of the iPPVs...

FB09 has two great matches before intermission, and then a bunch of disappointments.
The Big Bang has no real great matches in my opinion (some disagree), but was still a fun show to watch apart from one shitty brawl and one massive clusterfuck.
DBD8 has a fantastic main event and two very good semi-mains. The rest of the show ranges from total shit to barely mediocre.
GBH9 has some major pacing issues but is nonetheless a good, watchable show
FB10 is where ROH finally got their shit completely together with the iPPVs. The top two matches are both great, and the opener might be my favorite opener ever.

I've known of ROH for 5 years or so and when youtube came around, I started seeing the odd match on there and was impressed obviously. Then when it went came on HDNet I really going out of my way to catch the show for about the last year or so and I've purchased the last two ippv's. Now I'm just going back and starting to catch up on all the old shows.

Final Battle 2009 has got the be the biggest mixed bag in the history of ROH.

One on hand, there is an amazing, feud-ending tag match between Steenerico and The Young Bucks and an amazing beginning to one of the best storylines ever. Also, though the weakest Fight Without Honor, Kingston-Hero is a fitting end to their ROH feud with an incredible spot that must be seen. The two huge surprises (Steen's heel turn, the return of KOW) are two of the most exciting moments in ROH history.

On the other hand, there isn't a single other outstanding match. Adam Pearce lost his mind when he booked the main event to go broadway, but he really screwed the pooch when he booked 8 other matches on the undercard. Here is a year-ending show that should have been a wrestling classic, but instead is an overbooked circus show.